This invention relates to a spring operating mechanism for an electrical switch in which the energy stored in a spring mechanism causes an electrical power switching device to open or close.
FIG. 1 is a perspective schematic diagram showing a conventional spring operating mechanism as disclosed in Japanese Patent Laid-Open No. 59-163720 laid-open in March, 1984, and FIG. 2 is a partial detailed view of the same mechanism as seen in the direction of arrow A in FIG. 1.
The illustrated conventional operating mechanism comprises a drive mechanism 30 including a reversible electric motor 1, a speed reduction device 3 having an input shaft 3a and output shaft 3b, and a chain 2 for transmitting the rotation of the electric motor 1 to the input shaft 3a of the speed reduction device 3. On the output shaft 3b of the speed reduction device 3, a drive lever 4 is secured so that the drive lever 4 is operationally connected to the drive mechanism 30 for rotation about an axis of the output shaft 3b. The drive lever 4 has first and second engaging surfaces 31 and 32 which are circumferentially spaced.
The operating mechanism further comprises an actuating lever 5 rotatable about an axis of the pivot pin 11 which is in alignment with the output shaft 3b. Since the pivot pin 11 of the lever 5 is separate from the shaft 3b and rotatably supported at its opposite ends by bearings 17 and 18, the lever 5 is rotatable independently of the drive lever 4. The actuating lever 5 has a first and a second engagement surface 5a, 5b which are a pair of projections extending in opposite directions from both sides of the lever 5. When the drive lever 4 is rotated counterclockwise in FIG. 1, the engaging surface 31 of the drive lever 4 engages and pushes the projection 5a of the actuating lever 5 to rotate it counterclockwise about the pivot pin 11. When the drive lever 4 is rotated clockwise in FIG. 1, the second engaging surface 32 engages and pushes the projection 5a of the actuating lever 5 to rotate the actuating lever 5 clockwise.
The free end of the actuating lever 5 is connected to an energy storing mechanism 9 connected in an over-center relationship for selectively storing and releasing spring energy for opening and closing the electrical switch in accordance with the rotational movement of the actuating lever 5. In the illustrated embodiment, the energy storing mechanism 9 comprises a spring rod 6 pivotally connected at one end to the free end of the actuating lever 5 by a pivot pin 6a, and a flange 7 being secured to the rod 6. The other end of the rod 6 is slidably received within a cylinder 8 which has a flange 8a at its bottom. A pair of pivot pins 8b are attached to the flange 8a to pivotably support the bottom end of the spring mechanism 9 by an unillustrated frame. Between the flange 7 on the spring rod 6 and the flange on the cylinder 8, a compression spring 9a is disposed.
The positions of the pivot pin 11 for the actuating lever 5 and the pivot pin 8b at the bottom of the spring mechanism 9 are fixed and the pin 6a connecting the free end of the actuating lever 5 and the upper end of the spring mechanism 9 moves along the circle described by the free end of the actuating lever 5 about the pivot pin 11. The positions of these pins 11, 6a and 8b are selected so that the direction of the compressive force of the spring 9a acting on the actuating lever 5 through the spring rod 6 to rotate the lever 5 is changed when the knee point of the pivot pin 6a between the lever 5 and the spring mechanism 9 moves beyond a line "A" extending through the axis of the pin 11 and the axis of the pin 8b. In this context, the free end of the actuating lever 5 can be viewed as being connected to an energy storing mechanism 9 in a known over-center relationship.
The operating mechanism further comprises a driven lever 10 secured on a driven shaft 13 rotatably supported by a pair of bearings 19 and 20. The driven lever 10 has a first engaging surface 33 and a second engaging surface 34 which are circumferentially spaced and radially extending surfaces for being engaged by the second projection 5b on the actuating lever 5. When the actuating lever 5 is rotated counterclockwise in FIG. 1, the projection 5b of the actuating lever 5 engages the second engaging surface 34 of the driven lever 10 pushing the engaging surface 34 down to rotate the driven lever 10 counterclockwise. When the actuating lever 5 is rotated clockwise in FIG. 1, the engaging projection 5b engages and pushes the first engaging surface 33 of the driven lever 10 to rotate the driven lever 10 clockwise. The driven shaft 13 is in alignment with and rotatable about an axis aligned with the other rotational axes of the drive lever 4 and the actuating lever 5. Since the driven shaft 13 is independent and separate from other shafts and pins 8b and 11, driven lever 10 can rotate relatively independently of the other levers 4 and 5. The driven shaft 13 has also secured thereto a connecting lever 12 which is pivotally connected to one end of an operating rod 14. The other end of the operating rod 14 is connected to a movable contact 15 of the electrical switch for opening and closing the contacts.
Thus, when the actuating lever 5 rotates counterclockwise and the second projection 5b of the actuating lever 5 engages and pushes the engagement surface 34 of the driven lever 10, the driven lever 10 is rotated counterclockwise. This counterclockwise rotation of the driven lever 10 is transmitted and converted into a closing movement of the movable contact of the contacts 15 of the electrical switch through the driven shaft 13, the connecting lever 12 and the operating rod 14. When the driven lever 10 is rotated clockwise, the contacts 15 are separated.
Since the conventional spring operating mechanism is constructed as described above, when the drive lever 4 is rotated counterclockwise by the electric motor 1, it engages with the projection 5a of the actuating lever 5 to rotate the actuating lever 5 counterclockwise. During this movement, the free end of the actuating lever 5 pushes the upper end of the coil spring 9a downward through the spring rod 6 and the upper spring washer 7 to compress the spring 9a. During compression, the second projection 5b of the actuating lever 5 does not act on the engaging surface of the driven lever 10 due to the lost-motion arrangement between the two levers 5 and 10. When the connecting pin 6a of the actuating lever 5 moves right in FIG. 1 beyond the dead point line "A" extending through the axes of the pivot pin 11 and the support pins 8b of the flange washer 8a, the actuating lever 5 is rapidly rotated counterclockwise by the energy stored in the compressed coil spring 9a. Then the second projection 5b of the actuating lever 5 abuts the engagement surface of the driven lever 10 to rapidly rotate the driven lever 10 couterclockwise. This counterclockwise rotation of the driven lever 10 causes the counterclockwise rotation of the transmission lever 12 through the driven shaft 13 to cause the contacts 15 to close through the operating rod 14. The opening operation is achieved by rotating the electric motor 1 in the direction opposite to the case of the closing operation, whereby the transmission lever 12 is rotated clockwise to open the contact device 15 of the electrical switch.
Since the conventional spring operating mechanism comprises three separate axially aligned shafts, i.e., the output shaft 3b, the pivot shaft 11 and the driven shaft 13, for rotatably supporting independently the drive lever 4, the actuating lever 5 and the driven lever 10, each shaft must be rotatably supported by respective bearings. With this arrangement, not only a large axial space is required, but also a large distance between the drive lever 4, the actuating lever 5 and the driven lever 10 is required due to the axial space needed for installing the bearings. Therefore, the torque acting on the actuating lever 5 is increased, requiring more strength in the lever 5. Also, the number of parts is relatively large, resulting in an increased cost.